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Hillary Clinton and Bernie Sanders meet for a debate tonight, the first since the Vermont senator won the New Hampshire primary

Clinton is expected to energize her base supporter but also reach out to young voters, which have made up a core part of Sanders' support

(CNN)Hillary Clinton built one of the best-organized campaigns in history -- and so far, she has one narrow win and one blowout loss to show for it.

Now that Vermont Sen. Bernie Sanders has proven he's a serious threat to Clinton's bid for the Democratic presidential nomination, the race could get even thornier Thursday night when the two meet for their next debate in Milwaukee.

Here are five things to watch:

The race about race

Clinton's first post-New Hampshire move was a swift bid to lock in her support among African-Americans.

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The campaign dispatched Bill Clinton to Memphis and Chelsea Clinton to Flint, Michigan. It played up an influential state lawmaker's endorsement in South Carolina. And in her Tuesday night concession speech, Clinton issued a call to "break through the barrier of bigotry."

Showing no weakness at all with African-Americans is a crucial part of Clinton's strategy to calm nervous donors and supporters and eventually grind out a clear delegate lead by proving she appeals to the more diverse national Democratic electorate, while Sanders only plays in overwhelmingly white states.

Sanders, meanwhile, is speaking passionately about issues like criminal justice on the stump. He won support in recent days from former NAACP head Ben Jealous and award-winning writer Ta-Nehisi Coates.

Clinton's strength with African-American voters will be tested in South Carolina's February 27 primary, but first comes Nevada on February 20.

Once a sure thing for Clinton, her campaign is now sweating the state -- which offers Sanders a chance to prove his appeal extends south and west before South Carolina even votes.

The two both have clear reason to focus on minority voters -- and that outreach will be a key part of their debate-night strategies.

Revolution meets reality

The "political revolution" Sanders has called for is playing out in a way he never expected. No candidate in history has had his ability to go on national television and host a 30-second "fundraiser" by asking people to contribute on his website, and raise $6.3 million in 24 hours.

But as Sanders' pitches for free college tuition, Medicare-for-all health insurance and a $15-an-hour minimum wage have gotten more support, Clinton has grown more frustrated -- dismissing Sanders as unable to get the results he's promising.

This presents a key challenge for Clinton: She needs to challenge Sanders on policy. If she casts his supporters as living in a fantasy-land, she risks alienating them -- turning away the young people she needs to win over and putting herself at risk of looking like the embodiment of the "establishment" she laughs off.

How she presses the case that Sanders' policy proposals are unrealistic will offer perhaps the best insight into whether Clinton is truly retooling her message after losing New Hampshire.

Clinton's youth outreach

The exit polls showed a number of trouble spots for Clinton's campaign. She lost women. Democratic voters almost unanimously identified Sanders as more trustworthy and in touch with their problems. And she was beaten in every age group except those over 65.

Perhaps the most glaring problem Clinton faces is with young voters. By a 5-to-1 margin, they supported Sanders in New Hampshire.

That's the recipe for a loss, if not in the primary, then in the general election, where Democrats need young voters to turn out.

Clinton's surrogates Madeleine Albright and Gloria Steinem didn't help by criticizing young women not backing the former secretary of state -- throwing more fuel onto a simmering anger -- as traitors to the feminist cause for supporting Sander.

Clinton needs a new approach -- and Thursday night will be her first chance to debut it.

Sanders in the spotlight

Now that he has proven his ability to win states, Sanders will find himself the subject of much more intense scrutiny.

It's partly Clinton's fault. She didn't even say his name on the campaign trail for months, and her aides -- while arguing they were bracing for a tough primary battle -- did little to publicly damage Sanders.

He's shown little appetite to savage Clinton on controversies like her private email use and her hesitation at releasing transcripts of her paid speeches, even with Clinton practically daring him to attack.

But Sanders' most valuable political asset is his credibility -- particularly with young voters. How will he react when such a core element of his political being is called into question?

A sharper Clinton message

Sanders' focus on income inequality is, at different times, a strength (such as when to the topic of Wall Street reform comes up) and a weakness (when foreign policy dominates the news).

But give him this: Voters know exactly why he's running.

The same isn't always true of Clinton.

Clinton speeches often feel like a laundry list of specific policy prescriptions to the problems people face. And her biggest critique of Sanders is that his ideas are unattainable in a real-life Congress.

"I actually believe we talked about too many issues," Demers said. "She had a really broad discussion about every issue there was and Bernie Sanders stayed focused on one message. And that resonated."

Clinton's campaign knows it needs to end the muddled messages and find a unifying theme of her candidacy -- a simple, forward-looking explanation of why she is running for president. It'll be a focus as Clinton retools after New Hampshire, and Thursday night will be her first chance to try it out.